In a number of applications ranging from automotive to home automation and mobile computing, information retrieval on the amount of ambient light, e.g. in the photopic range of the electromagnetic spectrum, (i.e. light visible to the human eye) can be commercially interesting. Such information can for instance be used to control the light sources in an environment such that an appropriate tradeoff between comfortable lighting levels and energy consumption is established, to adjust the brightness of a mobile device display to prolong battery operating time, engage the headlights of a vehicle, e.g. when entering a tunnel, and so on.
In addition to photopic information, detection of UV and IR irradiation levels can also be of interest to either distinguish the type of the ambient light conditions, e.g. artificial light versus sunlight, or to deliver complete information on the environment's comfort level, such as the inclusion of information on UV exposure and the presence of radiant heat sources.
Photo-sensitive Si diodes may be used as light sensing elements. The light is absorbed in Si substrate by generating electron-hole pairs near the depletion region of a typically reversed-biased n+/p (or p+/n) diodes, these carriers are separated by the depletion region and as a result generate photocurrent that can be measured. The photocurrent is directly proportional to the light intensity; hence these devices can be used as light sensor transducers.
Si diodes in general have little wavelength selectivity and detect a rather wide spectrum that can include UV, visible as well as IR irradiation up to 1100 nm. Significant amount of literature exists on how it is possible to vary the sensitivity of the photodiodes to a given part of the spectrum using different diffusion depths of the dopants to form the diode junctions, formation of vertically-stacked diodes, as well as package- or casing-level filters applications. These methods, however, either do not deliver appropriate selectivity to the various parts of the spectrum and require a significant amount of signal post-processing, or only allow a single part of the spectrum to be sensed by each ALS (ambient light sensor) device.
With the ongoing diversification of electronic devices or electronic information gathering such as by RF tags on packaged articles, it is often desirable to include different types of sensors in a single IC. For instance, the detection of other environmental parameters, for instance temperature and humidity such as for HVAC (heating, ventilation and air conditioning) control in buildings and cars, could be particularly desirable.
Such multiple sensor ICs are known per se. However, most solutions are based on a system comprising multiple discrete sensors, which makes the system bulky and rather expensive. Also, the manufacturing process can be rather complex, especially when multiple light sensors for detecting different parts of the EM spectrum are to be integrated into a single IC. This negatively impacts on production yield and pushes up the price of the known good products.